In the present application, with the term “washing appliance” a washing machine or a combined washer-dryer is meant.
Many types of detergents to be used in the washing appliances are available nowadays.
The detergents can be classified in different groups, depending on their physical state: there are detergents in powder form, detergents in liquid or gel form and detergents in tablet form. The detergent in tablets can be divided in two sub-groups: tablets realized by compressed powder, which can also be further sub-divided in 2-in-1 detergent tablets, 3-in-1 tablets, 5-in-1 tablets, etc., and tablets in liquid form where the liquid is enveloped in a plastic membrane which dissolves in water.
A wash process of laundry or goods as performed by a washing appliance can be split in two phases. The first one is the washing cycle, also called main wash, and the second is the rinse phase or rinsing cycle.
Main wash represent the portion of the wash process during which the detergent is introduced within the appliance together with water to form a washing liquor. In this way, soil and dirt is removed from laundry and stabilized in the washing liquor. The key parameters involved in main wash are: temperature, amount of water, mechanical action, detergent type/amount and duration. In order to provide best results in washing performances vs. water amount and energy consumption, one or more of these parameters are generally optimized.
The rinsing cycle aims to remove the residuals of soil and detergent coming from the main wash. In many appliances, the rinsing cycle is performed stepwise, e.g. generally two or three rinsing steps are performed. Each step is commonly characterized by a defined amount of water, duration, and mechanical action.
The wash process is also often terminated by a final spinning cycle. Additional spinning steps might be present between consecutive rinsing steps during the rinsing cycle.
The rinsing cycle has a relevant impact on wash process water consumption. It covers more than 65% of the water filled in overall wash process. The rinsing cycle impacts also on the wash process time duration. For example, depending on the selected program, it could cover from 20% to 50% of the total wash process duration.
Rinse quality plays an important role in the customer perception; in particular it is highly undesired to retrieve residual of scum in the laundry after the wash process, and the increasing presence of allergies among users requires an efficient rinsing.
According to the known art, in certain conditions, the appliance could add an extra rinsing step in order to improve rinse quality. This additional rinsing step can be selected by the appliance's user or done by the appliance automatically, for example under critical condition such as a detection of high level of foam or when the quality of the rinse has to be improved for allergy or skin sensitive issues.
EP 1707663 discloses a procedure, for use on an automatic washing machine or washer/drier taking 2-4 kg of washing and a quick- or slow-dissolving liquid or powdered detergent in block or loose form, which includes periodic measurement of the electrical conductivity of the rinsing water. The measured values are compared with pre-determined threshold levels, and the duration of the rinsing and spin cycles of the washing program are adjusted to ensure that the use of rinsing water and intermediate spin speeds are kept to a minimum.